This invention relates to test apparatus, and more particularly to a system for uniformly tensioning long lengths of small diameter cables, up to several kilometers in length, while simultaneously exposed to simulated environments such as deep ocean conditions.
As fiber optic cable technology has evolved there has been an increasing interest in applying that technology to cables for use in the deep ocean. Testing has shown that optical fibers, because of the brittle nature of the glass, are subject to static fatigue when exposed to seawater and under strain. The glass will fail through brittle fracture at strains/stresses well below its normal limits because of corrosion effects in micro cracks on the fiber surface. Ocean cable designs are attempting to eliminate this problem by both removing the fiber from exposure to seawater (by using sealing jackets, tubes, etc.) and by adding strengthening members to reduce or eliminate strain in the fibers. There is a definite need to verify long-term performance of fiber optic cables for use in the ocean under high pressure, low temperature, and sustained cable strain in tension.
Before committing to production of thousands of kilometers of such cable envisioned for ocean systems, it is necessary to verify the performance of the completed cables under simulated conditions. In order to obtain accurate optical attenuation measurements on the low-loss cables ourrently available it is necessary to have continuous cable lengths of at least a kilometer or more under test. To simply stretch out such a length of cable in a linear ocean simulation facility would require extremely expensive new pressure testing facilities. There is presently no method for testing adequate lengths of cable without major expense in building very long pressure vessels. A means to uniformly tension these small cables while also efficiently packaging them into existing pressure vessel facilities is needed to provide significant cost savings.
It is an object of the present invention to provide an efficient system for uniformly tensioning long lengths of small fiber optic cables in simulated deep ocean conditions.